1. Field of Invention
The present invention generally relates to analysis of solutions. More particularly, the present invention relates to on-line automated matrix elimination, neutralization, or modification for trace contaminant analysis of solutions.
2. Discussion of the Related Art
Chemical solutions are used in various manufacturing processes in a multitude of industries, including the semiconductor, environmental, and pharmaceutical industries. A solution sample includes a matrix, defined herein as a liquid solution, suspension, or colloid, and a detectable amount of at least one analyte of interest. Examples of matrixes are diluted or concentrated acids, bases, oxidants, reducing reagents, solvents (such as alcohols, esters, ethers, glycols, ketones, amides, amines, or their mixtures), cleaning solutions, photoresists, strippers, and developers. Examples of analytes of interest are metals and their species.
The matrix has a pronounced effect on the quantification of trace constituents by modern analytical instruments. For example, a common problem is detecting analytes of interest in a matrix including one or more compounds of high ionic strength. Many times, the desired analyte peaks or signals are obscured by the large interfering peak of an undesired matrix ion. In many analytical instruments, the detector is saturated with matrix ion signals and is not able to distinguish the desired analyte signal.
In some cases, the desired signal is suppressed because the matrix ions compete with the desired analyte ions when ionization of the sample occurs for analysis purposes. Furthermore, matrix ions are increased during ion formation in electrospray ionization because in most cases, the matrix ions solvate or deprotonate the analyte of interest, resulting in less ion formation of the analyte of interest.
The composition or properties of a matrix may also change from process to process and during the life of the sample, which may then affect the recovery of an analyte from a complex matrix. Analyte speciation may further compound this effect. The stability of a sample/analyte may also change during analysis because of a changing thermal regime or photolytic effect. Thus, inaccurate analysis of a sample may occur because of the transitory nature of the matrix.
However, in many instances, accurately monitoring the analytes of a sample at a specific point in time during a process is highly desirable. For example, in semiconductor manufacturing processes, monitoring the elemental and molecular composition of solutions is of immense importance for producing reliable devices with high yield. Purity of these solutions during offline and online processes is very important as well. The continuous decrease in the geometry of devices requires increased control of the contaminants in solution, especially those solutions that come in direct contact with the electronic circuitry during device fabrication.
To reliably measure the elemental and molecular composition of samples at a parts-per-trillion level is not only complicated but also laborious and time consuming. The biggest challenge is to maintain the integrity of the sample starting from the sampling (i.e., collection) to the end of the analysis.
First, most matrixes are dynamic in nature, i.e. the components of a solution continually react with other components and can change over time. Thus, by the time a sample reaches a laboratory for analysis, the sample may not be in exact formulation as it was at the time of collection.
Second, many matrixes are strong absorption media for airborne soluble contaminants so if samples are exposed to air at any stage during sampling, transportation, or analysis, the matrix of the sample may be altered or contaminated.
Third, the cleanliness of the sampling containers is very important and a large amount of time and money is spent to clean sampling containers. The amount of time the sample is allowed to sit in the sampling container before being analyzed can also effect the analysis outcome. It has been reported that even the cleanest of sampling containers can leach out many undesirable contaminants.
Fourth, offline elimination, neutralization, or modification of matrixes generally pose a high risk of contamination that can affect the integrity of the sample for the reasons stated above.
At present, for routine monitoring of matrixes, samples are collected from sources in a protected clean environment in pre-cleaned containers. The containers holding the samples are delivered to the laboratory for measurements of the elemental or molecular constituents by various analytical instruments. It can take between 4 to 24 hours before the analysis results are received by process personnel. Accordingly, in most cases, if a problem is detected, such as impurities in the sample, processing of defective product will have occurred for some time and the cost related to low yield will be high. As a result, many industries are placing a major emphasis on on-line measurements to provide substantially real-time analysis.
In common practice, depending on the nature and concentration of the matrix, various analytical laboratories have developed their own methods to test these matrixes. For example, some laboratories dilute the sample to reduce the effect of the matrix but by doing so many ultra low trace level contaminants may not be detected. Other laboratories eliminate the matrix by heat and/or evaporation but by doing so potentially lose the integrity of the sample constituents.
Therefore, a need exists for a method and apparatus for accurate elemental and molecular analysis of process solutions, particularly for trace metal contaminants.